When i try to put textures, everything goes black
That is your AO image that you made in the tutorial, and loading the image that you painted in the UV Image Editor doesn't automatically apply it to the mesh object - load it in the material texture slot so that it will be used in your mesh. Looks like the tutorial skipped that part.

Also, if your mesh turns black when trying to load the new texture, try adding lights (lamps) to your scene if you are in GLSL.